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Tag Archives: April 13

Scientists call for plans to change asteroid’s path.
Developing technology could take decades.

Alok Jha
The Guardian, Tuesday 6 December 2005

In Egyptian myth, Apophis was the ancient spirit of evil and destruction, a demon that was determined to plunge the world into eternal darkness.

A fitting name, astronomers reasoned, for a menace now hurtling towards Earth from outerspace. Scientists are monitoring the progress of a 390-metre wide asteroid discovered last year that is potentially on a collision course with the planet, and are imploring governments to decide on a strategy for dealing with it.

Nasa has estimated that an impact from Apophis, which has an outside chance of hitting the Earth in 2036, would release more than 100,000 times the energy released in the nuclear blast over Hiroshima. Thousands of square kilometres would be directly affected by the blast but the whole of the Earth would see the effects of the dust released into the atmosphere.

And, scientists insist, there is actually very little time left to decide. At a recent meeting of experts in near-Earth objects (NEOs) in London, scientists said it could take decades to design, test and build the required technology to deflect the asteroid. Monica Grady, an expert in meteorites at the Open University, said: “It’s a question of when, not if, a near Earth object collides with Earth. Many of the smaller objects break up when they reach the Earth’s atmosphere and have no impact. However, a NEO larger than 1km [wide] will collide with Earth every few hundred thousand years and a NEO larger than 6km, which could cause mass extinction, will collide with Earth every hundred million years. We are overdue for a big one.”

Apophis had been intermittently tracked since its discovery in June last year but, in December, it started causing serious concern. Projecting the orbit of the asteroid into the future, astronomers had calculated that the odds of it hitting the Earth in 2029 were alarming. As more observations came in, the odds got higher.

Having more than 20 years warning of potential impact might seem plenty of time. But, at last week’s meeting, Andrea Carusi, president of the Spaceguard Foundation, said that the time for governments to make decisions on what to do was now, to give scientists time to prepare mitigation missions. At the peak of concern, Apophis asteroid was placed at four out of 10 on the Torino scale – a measure of the threat posed by an NEO where 10 is a certain collision which could cause a global catastrophe. This was the highest of any asteroid in recorded history and it had a 1 in 37 chance of hitting the Earth. The threat of a collision in 2029 was eventually ruled out at the end of last year.

Alan Fitzsimmons, an astronomer from Queen’s University Belfast, said: “When it does pass close to us on April 13 2029, the Earth will deflect it and change its orbit. There’s a small possibility that if it passes through a particular point in space, the so-called keyhole, … the Earth’s gravity will change things so that when it comes back around again in 2036, it will collide with us.” The chance of Apophis passing through the keyhole, a 600-metre patch of space, is 1 in 5,500 based on current information.

There are no shortage of ideas on how to deflect asteroids. The Advanced Concepts Team at the European Space Agency have led the effort in designing a range of satellites and rockets to nudge asteroids on a collision course for Earth into a different orbit.

No technology has been left unconsidered, even potentially dangerous ideas such as nuclear powered spacecraft. “The advantage of nuclear propulsion is a lot of power,” said Prof Fitzsimmons. “The negative thing is that … we haven’t done it yet. Whereas with solar electric propulsion, there are several spacecraft now that do use this technology so we’re fairly confident it would work.”

The favoured method is also potentially the easiest – throwing a spacecraft at an asteroid to change its direction. Esa plans to test this idea with its Don Quixote mission, where two satellites will be sent to an asteroid. One of them, Hidalgo, will collide with the asteroid at high speed while the other, Sancho, will measure the change in the object’s orbit. Decisions on the actual design of these probes will be made in the coming months, with launch expected some time in the next decade. One idea that seems to have no support from astronomers is the use of explosives.

Prof Fitzsimmons. “If you explode too close to impact, perhaps you’ll get hit by several fragments rather than one, so you spread out the area of damage.”

In September, scientists at Strathclyde and Glasgow universities began computer simulations to work out the feasibility of changing the directions of asteroids on a collision course for Earth. In spring next year, there will be another opportunity for radar observations of Apophis that will help astronomers work out possible future orbits of the asteroid more accurately.

If, at that stage, they cannot rule out an impact with Earth in 2036, the next chance to make better observations will not be until 2013. Nasa has argued that a final decision on what to do about Apophis will have to be made at that stage.

“It may be a decision in 2013 whether or not to go ahead with a full-blown mitigation mission, but we need to start planning it before 2013,” said Prof Fitzsimmons. In 2029, astronomers will know for sure if Apophis will pose a threat in 2036. If the worst-case scenarios turn out to be true and the Earth is not prepared, it will be too late. “If we wait until 2029, it would seem unlikely that you’d be able to do anything about 2036,” said Mr Yates.

If the asteroid Apophis hits Earth in 2036, it could slam into the Pacific Ocean, generating a tsunami that could devastate the west coast of North America (Illustration: Don Davis/NASA)

In 2004, NASA scientists announced that there was a chance that Apophis, an asteroid larger than two football fields, could smash into Earth in 2029. A few additional observations and some number-crunching later, astronomers noted that the chance of the planet-killer hitting Earth in 2029 was nearly zilch.

Now, reports out of Russia say that scientists there estimate Apophis will collide with Earth on April 13, 2036. These reports conflict on the probability of such a doomsday event, but the question remains: How scared should we be?

“Technically, they’re correct, there is a chance in 2036 [that Apophis will hit Earth],” said Donald Yeomans, head of NASA’s Near-Earth Object Program Office. However, that chance is just 1-in-250,000, Yeomans said.

The Russian scientists are basing their predictions of a collision on the chance that the 900-foot-long (270 meters) Apophis will travel through what’s called a gravitational keyhole as it passes by Earth in 2029. The gravitational keyhole they mention is a precise region in space, only slightly larger than the asteroid itself, in which the effect of Earth’s gravity is such that it could tweak Apophis’ path.

“The situation is that in 2029, April 13, [Apophis] flies very close to the Earth, within five Earth radii, so that will be quite an event, but we’ve already ruled out the possibility of it hitting at that time,” Yeomans told Life’s Little Mysteries. “On the other hand, if it goes through what we call a keyhole during that close Earth approach … then it will indeed be perturbed just right so that it will come back and smack Earth on April 13, 2036,” Yeomans said.

The chances of the asteroid going through the keyhole, which is tiny compared to the asteroid, are “minuscule,” Yeomans added.

The more likely scenario is this: Apophis will make a fairly close approach to Earth in late 2012 and early 2013, and will be extensively observed with ground-based optical telescopes and radar systems. If it seems to be heading on a destructive path, NASA will devise the scheme and machinery necessary to change the asteroid’s orbit, decreasing the probability of a collision in 2036 to zero, Yeomans said.

There are several ways to change an asteroid’s orbit, the simplest of which is to run a spacecraft into the hurtling rock. This technology was used on July 4, 2005, when Deep Impact smashed into the comet Tempel 1.

The asteroid Apophis was discovered on June 19, 2004. It will fly within 18,300 miles of Earth on April 13, 2029, but poses little risk of impact. CREDIT: UH/IA

This story was updated at 4:55 p.m. ET.

Russia is considering a plan to launch a spacecraft capable of moving a huge asteroid in a bid to protect Earth from an impact, but the target space rock poses virtually no threat to our planet and moving it could actually make matters worse, experts say.

American astronomer Paul Chodas, part of NASA’s Near-Earth Object (NEO) Program Office, said Wednesday that claims by a top Russian space official that the asteroid Apophis would definitely crash into Earth around 2036 are inaccurate.

Anatoly Perminov, chief of Russia’s Federal Space Agency, said today that his agency will soon hold a special meeting to discuss a potential mission to Apophis, according to Russian wire reports. Perminov spoke on the Voice of Russia radio and said experts from the United States and other nations and space agencies would be able to join the project once the details are set.

Perminov said he had heard of Apophis’ threat to Earth from a scientist who had calculated that the asteroid was getting closer and would “surely collide with Earth in the 2030s,” according to Russia’s RIA Novosti news service.

Apophis is actually expected to fly harmlessly by Earth on April 13, 2036 and come within 18,300 miles (29,450 km) of the planet at its closest approach.

In October, Chodas and NEO office colleagues at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., announced that the odds of Apophis slamming into Earth when it swings by had dropped to a low, 1-in-250,000 chance. Those odds improved on earlier studies that predicted a 1-in-45,000 chance of an impact.

The asteroid’s second near pass by Earth comes in 2068, when it has a three-in-a-million chance (or about 1-in-333,000) of endangering the planet.

Chodas told SPACE.com that Apophis will remain a top impact risk for Earth over the long term, say over the next million years. But sending a spacecraft to intentionally tweak the asteroid’s orbit in the short term, when it poses little risk, carries its own dangers.

“You have the potential of increasing the impact probability with failures in the mission,” Chodas said. “You could make matters worse.”

An exploratory mission to study Apophis, and perhaps return a sample, could be a vital resource for any future deflection efforts, he added. Knowing the composition of an asteroid would likely play a large part in deciding exactly how to attempt to deflect its course.

Perminov did not mention the recent Apophis impact risk estimates or elaborate on exactly how a Russian spacecraft may try to move the asteroid, though he did say nuclear weapons would not play a role.

“No nuclear explosions [will be carried out], everything [will be done] on the basis of the laws of physics,” RIA Novosti quoted Perminov as saying. Past studies have weighed using everything from nuclear weapons and spacecraft’s gravity to rocket engines, robotic swarms and old-fashioned paint to protect Earth from space rocks.

Don Yeomans, head of NASA’s Near-Earth Object Program Office, told SPACE.com that Russia’s interest in tackling potentially threatening asteroids in general is a good sign.

“While Apophis is almost certainly not a problem, I am encouraged that the Russian science community is willing to study the various deflection options that would be available in the event of a future Earth threatening encounter by an asteroid,” Yeoman’s said in an e-mail. “We haven’t found one yet but it does make sense to study deflection options in advance.”

Apophis has been a poster child of sorts for the risk near-Earth objects pose to life on our planet because of the back-and-forth over when it could strike.

“Its orbit nearly intersects the Earth’s orbit,” Chodas said.

At one time, early projections gave Apophis an alarming 1-in-37 chance of crashing into Earth, sparking public fears of an imminent disaster. That’s about a 2.7 percent chance of an impact somewhere on Earth. Better observations of Apophis since then have allowed astronomers to refine their projections of its trajectory and quell hysteria over its hazard to Earth.

Apophis is about 900 feet (270 meters) long and larger than two football fields overall. The asteroid is massive enough to create significant devastation to a region if it ever did strike Earth. But it is not large enough to create a global catastrophe, NASA scientists have said.

Tracking Apophis has been challenging because of its orbit, which lies within the orbit of Earth with the space rock hard to spot at times. The asteroid is expected to come back within observation range of Earth (about 9 million miles) in late 2012 and early 2013.

“The additional optical and radar data taken then will almost certainly remove any possibility of an Earth collision in April 2036,” Yeomans said. “To my mind it would make sense to wait until 2013, refine the orbit and in the very unlikely event that the impact probability increases, then begin planning possible deflection options.”

Still, Russian space officials apparently consider Apophis a significant threat to life on Earth despite the low odds of an impact.

“People’s lives are at stake. We should pay several hundred million dollars and design a system that would prevent a collision, rather than sit and wait for it to happen and kill hundreds of thousands of people,” Perminov said, according to RIA Novosti.